1. Field of Invention
Hop flavors, compositions thereof, unreduced alpha and isoalpha acids, reduced alpha and isoalpha acids, removal of undesirable odor-forming impurities therefrom, hop flavors which do not contain such impurities, flavoring of beer including ale therewith.
2. Prior Art and the Invention Broadly Stated
Hop flavors of the isoalpha acid types enumerated under FIELD OF INVENTION have attracted widespread interest in recent years for use in the controlled and standardized flavoring of beer including ale, especially by post-fermentation treatment. The present invention involves the discovery that certain hitherto-unrecognized undesirable odor-forming impurities (the exact structure and nature of which is yet unknown) exist in all of these hop flavors which, if allowed to remain, in time give rise to undesirable aromas of a fruity, estery, fatty or sour nature upon standing or storage of beers flavored post-fermentation therewith. The present invention accordingly also involves the removal of such undesirable odor-forming impurities from the starting hop flavor with production of a purified hop flavor which is essentially free of undesirable amounts of such odor-forming impurities and hence also free of such odor- or aroma-contaminating tendency when employed to flavor beer post-fermentation. The method for eliminating the said impurities involves their extraction from the hop flavor into water at a pH above about 4, preferably above about 6 or 7, the exact preference in pH depending upon the acidity of the hop flavor being extracted, sometimes in the presence of solvent such as residual carbon dioxide, hexane, or lower-alkanol such as ethanol, and preferably in the presence of a salt for purposes of keeping most if not all of the hop flavor itself in the organic phase, an important economic consideration. Although the PRIOR ART has employed highly-acidic (pH 2 and below) aqueous extractions of such starting hop flavors to remove previously-recognized impurities such as metals, tannins, and sugars, extractions at such low pH levels will not and does not remove the odor-forming impurities discovered and eliminated according to the present invention. Neither does the procedure of the prior art, which has been used to extract crude isomerized whole hop extracts with water to produce an aqueous phase, still containing the impurities together with small amounts of isoacids which will dissolve in the water at the pH level employed, eliminate these impurities or provide a suitable post-fermentation flavor, even though such solutions have been suggested for flavoring of beer post-fermentation and are reported to be non-haze-forming. (Westermann U.S. Pat. No. 3,798,332).